Referring to FIGS. 7 and 8, the prior art twisting spanner is illustrated. In operation, the handle 30 must be twisted and the step of twisting setting value is set according to a scale 31 and a spring 33 between a push post 32 and a supporting seat 20 is compressed. After setting, the handle 30 is fixed. In operation, a pin 44 at one end of a main arm 41 is twisted to press the roller 21 of the supporting seat 20. Likewise, the roller 21 provides a react force until the force from the spanner is over the twisting force. The roller 21 will release from the pin 44 and the main arm 41 returns rapidly. Thus an end 41 of the main arm 41 will knock the wall of the cover 42 so as to have a knocking sound to inform the user not to increase the applied force for preventing the spanner from destroy.
However since the prior art spring 33 is long, as shown in FIG. 8, to cause the wall of the supporting seat 20 is smooth and the spring 33 can be compressed easily, the inner diameter is greater, but as a result, the spring 33 will bent. As a result the twisting value is not accuracy and is not stable. Thereby the spring 33 will fatigue and not return to the original position. That is to say that the moving length of the push post 32 driving by the handle 30 is long so that the twisting force cannot be set accuracy. It has an error of about 4%. The longer the spring, the greater the error. Furthermore, in the prior art, the supporting seat 20 has a hard ball to contact the wall of the cover 42 so that the wall of the cover 42 will be destroyed.
Moreover one end of the supporting seat 20 has a ball 23 ejecting the wall of the buffer cove 42 so that the supporting seat 20 will tilt so that the supporting seat 20 will be buckled. As a result the twisting value is not accurate.